ABSTRACT / SUMMARY The complexity of organisms does not correlate with the number of protein encoding genes. Regulatory mechanisms have contributed to the diversification of gene function during evolution. Alternative splicing is a posttranscriptional mechanism that explains how single genes can produce more than one transcript due to the inclusion or exclusion of specific regions. In humans, more than 90% of genes undergo alternative splicing, consistent with the increased cellular and functional complexity of higher eukaryotes. Genome wide studies have exponentially increased the number of splicing isoforms and networks with completely unknown functions. Genes encoding membrane trafficking proteins are developmentally regulated by alternative splicing specifically in striated muscles between birth and adulthood. This finding raises the question of the physiological implications of this level of regulation. Understanding the role of splicing regulation in the expression and function of proteins involved in trafficking and membrane dynamics is the knowledge gap inspiring our project. The scientific premise of this R01 proposal is that alternative splicing regulation of trafficking proteins plays key developmental roles in cells, tissues, and organs. The fundamental question asked in this proposal is how alternative splicing controls membrane trafficking in specific tissues and cell types. We will tackle this question in two aims: (aim 1) what are the regulatory mechanisms that coordinate these splicing transitions? (aim 2) what are the functional consequences of splicing regulation of membrane trafficking genes? In Specific Aim 1, we will identify the role of two RNA-binding proteins (PTBP and QK) and epigenetics in splicing regulation of membrane trafficking genes in muscle cell differentiation. In Specific Aim 2, we will determine the downstream functional consequences of alternative splicing regulation of the membrane trafficking gene Trip10 (Cdc42 interacting protein-4, CIP4) utilizing cell culture experiments and animal studies. Overall, after completion of this project we will have identified the molecular mechanisms involved in alternative splicing regulation of membrane trafficking proteins, and their physiological significance.